Grease and flour 2 (9-inch) cake pans. In a medium bowl or on a piece of waxed paper, sift together flour, cocoa, baking soda, baking powder, and salt; set aside. In a large bowl, cream together sugar and butter. Beat in eggs, 1 at a time. Alternately add flour mixture and buttermilk. Beat in food coloring and vinegar, then add vanilla. Spread the batter evenly in the pans.
Bake for 20 to 30 minutes or until a wooden toothpick inserted into the center comes out clean. Turn out onto a rack to cool.
For the Frosting:
In a large bowl, combine the cream cheese and butter. Beat in confectioners' sugar until fluffy. Beat in vanilla. Stir in pecans. Use frosting to fill and ice cake.